Electrical switch instrument



United States Patent [72] Inventor Randall G011 Weston, Conn. [21] Appl. No. 742,605 [22] Filed July 5,1968 [45]- Patented Dec. 15,1970 [73] Assignee Dresser Industries, Inc.

Dallas, Tex. a corporation of Delaware [54] ELECTRICAL SWITCH INSTRUMENT 11 Claims, 9 Drawing Figs.

52 us. Cl 200/56, 335/206 [51) Int. Cl. ..G0ld 13/26 [50] Field of Search..... 200/56; 335/206; 337/322, 323; 307/885 [5 6] References Cited UNITED STATES PATENTS 1,762,491 6/1930 Thomrnes 200/56(X) 2,140,708 12/1938 McCabe 337/322(X) 2,456,062 12/1 948 lwanski 200/56(X) 2,663,806 l2/l953 Darlington 307/38.5(X) 3,056,865 10/1962 Reardon et al. 200/56 3,196,286 7/1965 Darack 307/885 3,225,622 12/1965 Du Bois et al 200/56(X) Primary Examiner-H. 0. Jones Attorneys-Robert W. Mayer, Daniel Rubin, Peter J. Murphy,

Frank S. Troidl, Roy L. Van Winkle and William E. Johnson, Jr.

ABSTRACT: A presettable' electrical switch instrument having condition responsive sensitivity for opening and closing an electrical circuit. A magnet, movable in response to condition changes, actuates a reed switch which triggers a switching module for appropriate actuation of the circuit to be con-- trolled. The specific component assembly enables instrument operation at extremely close preset differentials while affording enhanced selective interchangeability between normally open and normally closed operation.

PATENTED nan 519m 3548.129

SHEET 2 OF 3 INVENTOR 5 RANDALL GOFF l8 69, 2%.; 51% k ATTORNEY PATENTED DEC] 519m 3,548,129

SHEET 3 [1F 3 INVENTOR F 9 RANDALL GOFF ATTORNEY 1 I ELECTRICAL SWITCH INSTRUMENT CROSS REFERENCES TO RELATED APPLICATIONS BACKGROUND or THE INVENTION l. The field of art to which the invention pertains includes the art of electricity, circuitmarkers andbr'eakers as specifically including the art therein pertaining to switch instruments operative by fluid pressure or other force and'motion-producing devices.

2. Condition responsive switch instrumentsfor various control purposes are wellknown in the industryand are available from any sources of manufacture. Common among the switch instruments commercially marketed are those in which the switching element comprises either a mercury tilt bulb or a magnetically actuated member with mercury wetted contacts which appropriately'make or break a circuit in response to condition changes to which the condition responsive element is sensitive. Frequent requirements of these switches are that the contacts be hermetically sealed and/or that they be-operative between'differential limits to both make and break the circuit at conditions determined and field 'set'in accordance with customer requirements. While these priordevices work well under conditions Commonly-encountered, they are inherently characterized by the inability to be satisfactorily serviceable under certain conditions required for specialized applications.

By way of example, the magnetically actuated type instrument has a limited current-carrying capacity imposed by the small contacts and'light moving parts. High current ratings are specifically, the invention relates to a control switch instrument employing solid state components and operative in response to a force transmitting unitwithin differential limits decreased below that which has been possible with switch instruments previously known. In addition the switch hereof simultaneously affords a higher current carrying capacity than was possible with similar prior art instruments while eliminating the objections to mercury and enabling a field set adjustment for normally closed or normally open operation without requiring a mechanical interchange of the linkage mechanism.

In accordance herewith, the instrument is comprised of a reed switch carrying a relatively small current and actuated by a relatively light, permanent magnet movable by a Bourdon tube in response to pressure changes in the system being controlled. The reed switch in turn triggers or pilots a solid state switching module having a relatively high current capacity and connected to the circuit in which the system condition is to be maintained. Because of the light weight and low forces innot possible to obtain at the same time it is desired to minimize differential between switching points owing to the force and motion differential involved. As a practical-measure, such instruments are limited to a current rating of about one-half amp in order to obtain switching differentials of 2perce'nt or less. The mercury-type switch, on the other hand,'can carry heavier currents but requires a gravity shifting of the mercury glob to and from contacts in response to tilt movement by either a pressure or temperature sensitive element: Accordingly, a minimum range of operation is required for shift of the mercury and differential operation less than a minimum of about 5.v

percent is impossible to obtain. 1

Moreover, because these switch instruments are in such widecommercial use, they are mass produced to be readily I available for meeting the requirements of the markets they are to serve. However, control situations for which these instruments are employed alternatively require thatthey be operative as either normally open, i.e. in open circuit relation in the absence of a preapplied closing force, or be normally closed, i.e., in closed circuit relation in the absence of a preapplied opening force. Accordingly, it has been necessary for manufacturers to make and for suppliers to stock separate switch instruments providing both types of switching action to satisfy customer needs on demand. Various techniques have been employed to render-the operation interchangeable including the obvious technique of instrument disassembly to turn the mercury bulb end for end. An'improved technique forobtaining interchangeable operation is disclosed in .the aforementioned cross referenced application Serfi No. 671,438 requiring a-minimum degree of manual component interchange in the linkage system.

At the same time, certain industries cannot tolerate the presence of mercury while other .industrial applications frequently require the switch to have a high current capacity, neither objective of which could be conveniently satisfied by the prior type switch instruments. I

SUMMARY volved in the actuating mechanism, extremely close differential performance, substantially less than previously possible with prior art devices, is easily and accurately achieved. By simply rotating the reed switch manually on its mount through a small angular displacement whereby the magnet either approaches or departs from the reed switch in response to a given directional movement of the Bourdon tube, the entire instrument can be readily and simply adapted in the field for either normally open or normally Closed circuit response.

It is therefore an object of the invention to provide a novel control switch instrument sensitive to condition changes.

It is the further object of the invention to provide a novel differentially operable control switch'instrument capable of creased ease and without either mechanical substitutions or changes as has been customary in the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS.

FIG. 1 is a front. view partially broken away illustrating an exemplary control instrument employing a switch operable in accordance with the invention hereof;

FIG. 2 is an end elevation of FIG. 1 taken sectionally through the cover;

FIG. 3 illustrates the relationship of the component elements for normally open operation of the switch;

FIG. 4 is a fragmentary view similar to FIG 3 and illustrating the relationship of the component elements for normallyclosed operation of the instrument;

FIG. 5 is an end elevation of the pivotal magnet supporting bracketf FIG. 6 is an enlarged side elevation of the reed switch subassembly;

FIG. 7 is a sectional elevation taken lines 7-7 of FIG. 6;

FIG. 8 is a sectional view of the solid state switch module subassembly; and I FIG. 9 is an electrical circuit diagram partially schematic illustrating the circuit relation between the solid state switch assembly and the reed switch components;

Referring now to FIGS. 1 and 2, there is illustrated a condition responsive switchinstrument which generally may be of a type disclosed in U.S. Pat. No. 3,225,622 .and incorporated substantially along the herein by reference although not to be considered a limitation closed in the front open end of the housing is a transparent I is a potting compound 84 such as an epoxy or silicone which Within the casing is supported a Bourdon tube 20 connected in fluid communication at its fixed end to socket 19 for receiving fluid pressure supplied thereto. The free end of the tube 20 is connected to one end of a pivot link 21 which has its other end connected via a pin 22 and slip washer 23 to a beam 26. As can be seen, the beam 26 comprises a generally elongated sheet metal member having an elongated slot 27 extending longitudinally thereof. Mounted on this portion of the beam is a clamp 28 having a generally U-shaped cross section to embrace the beam and is held thereon by clamp screw 30 extending through the slot 27 and which can be adjustably located therein. The screw 30 includes an extension in the form of a pin 32 supported at its opposite end in a secured bracket 33 to provide a fulcrum pivot for'the beam in response to forced movement transmitted from the Bourdon tube. Also provided in the instrument are arms 35 and 36 by which the module 44. The latter preferably comprises a Triac which performs the switching operation via leads 45 and 46 connected to the system being controlled. 7

' Bracket assembly 40. is more fully shown in FIGS. 35 which will now be-described. The assembly includes a bracket arm 50 secured at its lower end to a U-shaped base 51 having depending legs through which to laterally receive a fixed shaft 52 defining a pivot axis thereof. A slip washer 53 laterally secures the base to the shaft. Connecting the base to the beam 26 is a hand compressible spring clip55 supported on laterally extending pivot pin 56 and having longitudinal, openings therein in which to secure the leftmostend of the beam as viewed in FIG. 3. The upper portion of the bracket arm is hooked over to provide a gap 57 between spaced legs 58 and 5 9. interposed between the legs to limit bracket pivot in either direction is a fixed shaft 60 extending secured from the back wall 18. At the topmost portion of the bracket arm is a' laterally offset foot 63 on which elongated magnet 64' is secured at its underside. A counterclockwise movement of linage 21 caused by the Bourdon tube likewise produces a counterclockwise movement of the bracket arm 50. Maximum arm movement is defined by the gap distance 57 until leg 59 is displaced into engagement against shaft 60 at which time foot 63 and magnet 64 are at the location shown dashed. In a preferred embodiment the magnet 64 is of about one-fiftieth ounces being about one-halfinch in length with a cross section of approximately l/l6 X l/l6 inches. By virtue of its supported spacing from the pivot axis, minimum mass of the magnet avoids undesirable moment forces when operative as in FIG. 3.

The reed switch assembly 42 as shown in FIGS. 6 and 7 includes a plastic housing 70 having a clevis connection 71 at its lower section for mounting on the shaft 60. Screw 72 extending through washer 77 and speed nut 78 secures the housing onto the shaft in a desired position as will be explained. At the upper end of the housing, there is a recess supporting a tubular envelope 73 containing the reed switch 74 having outwardly extending leads 75 and 76. These latter leads in turn are each solder connected to wire leads 79 and 80 connected to a terminal board 81 (FIG. 9) and which are effective for triggering switching module 44. Sealing envelope 73 within the housing has the desirable properties of electrical insulation, moisture proof and otherwise provides physical protection to the reed switch and lead wires.

Switching module 44 can best be understood by reference to FIGS. 8 and 9 and is of a solid state unit type providing a switching Triac with gate resistor and spike filter. In a preferred embodiment, this unit is commercially available as G. E. model SC 45 B characterizedby voltage and current ratings appropriate for these purposes in a general industrial control switch instrument. The .unit includes an enclosing aluminum case 87 housing components including a Triac 88 mounted to the case through insulating bushing 86 via nut 89 and insulating washers 90 and 91.

Lead 94 connects the nut end 89 of the Triac to terminal board 81 whereat'it connects to reed switch trigger lead 79. Reed switch lead 80 likewise connects -to' the terminal board whereat it ties in=with-lead 93 which completes the trigger or gate circuit through gate resistor 92 to gate terminal 101 on the Triac. The spike suppression filter, for protection against line transients, comprises capacitor 95 and resistor 96 which.

are connected in series through lead 97 between. the Triac main control terminals 102 and 103. External leads 45 and 46 are connected at terminal board 81 to leads 98 and 94 r'especv tively.

To electrically insulate and physically protect the entire assembly 44, it is potted with an insulating compound such as an epoxy or silicone and otherwise conforms to the requirements of the Underwriters Laboratory. Triac heat is, transferred to the air by way of the heat sink comprised of the aluminum case 87 and potting compound aswellas to the back of hous-' ing 12.A coating'of heat-conductive compound is employed to reduce the thermal resistance at the joint-between the as sembly 44 and switchh ousing 12. Y

In operation, movement of the Bourdon tube in response to pressure changes in the system being controlled, effects movement of beam 26 and consequent pivoting of'bracket assembly 42 about pivot axis 52. The reed switch assembly 42 is mounted on post 60 set with'the reed switch 74 prepositioned proximally corresponding at either extreme travel limit to be effected by bracket 50 in its pivotal displacement. As shown in FIG. 3, the reed switch is displaced from magnet 64 fat'a position representing a normal operation of the controller such as normally open, until the magnet is pivoted counterclockwise to energize the reed switch by the imposed magnetic field thereof. That is, for normally open operation this latter condition represents movement of the magnet toward the reed switch, for example, in response to increased system pressure requiring the circuit to be closed. a

To change controller operation from .the normally open condition of FIG. 3 to the normally closed condition of FIG. 4, the reed switch need only be rotated on post 60 through a small angle until within the magneticfield 0f magne t64 in the normal condition of the instrument, i.'e. the reed switch is constantly actuated in' the absence of increased pressure movement exerted by the Bourbon tube. Subsequent movement of the Bourbon tube in response to a pressure rise effects pivotal displacement of bracket 50 removing the magnet fromfthe reed switch to the position shown dashed in FIG. 4 permitting the reed switch to open. Therefore, by the simple angular presetting of the reed switch on post 60, operation of the switch can be easily and optionally interchanged between normally open and normally closed operation of the control instrument.

By the above description thereis disclosed a novel condition responsive control switch instrument for operating system equipment at desirable differential limits. Since making and breaking contact can be effected with themere slight shift of the magnetic field by appropriate displacement of the magnet, operation at minimum differential limits are possible which are substantially less than permitted by prior type switch controllers. At the same time, since the operating contacts need not carry the system current but operate as an intermediate required operating condition for either normally closed or normally open operation can be manuallyidone in the field with the Inere'useol' a screw driver without requiring any substitution or replacementsof mechanical. components. This latter feature not only lends versatility to the instrument but highly simpliliesthe problem which has previously .been regarded as dilficult in production equipment. Notwithstanding the advantageous features afforded by the controller switch hereof. its manufacturing cost is comparably less by virtue of the simplified ascmbly by which these improved results are attained v Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing fromthe scope thereof. it is intended that all matter contained in the drawings and specification shall be interpreted as illustrative nndnotina'limitingsense; if

a t I. In a condition responsive electrical controller instrument operative withindil'l'crential'condition limits for controlling a w conditionso be maintained and including a housing, diflerential limit means comprising avffirst operable limit representing a first condition magnitude-lat :which a control operation can occur. a second operable lirnit'v different than said'first operable limit and representing a second condition magnitude at whichra controlioperation can occur and between which limits an operative condition existing at one operable limit is maintained untilthe .other operable limit is netic member. 7

5. In the condition responsive controller instrument of claim 2 including presettable means-permitting interchangeability between relative operating locations of reed switch and magnetic member to optionally prcse'lect between normally open and normally closed operation-of the instrument at the difierential conditions preset by said set'table means.

6; In the condition responsive controller instrument of claim in which said prcsettable means includes a support for said reed switch, and means permitting displacement of said reed switch on said support between a first position relative to the magnetic member in which, the instrument is operative as normally closed and a second position relative to the magnetic mcmber in which the instrument is operative as normally e. :a magnetic-member movable by force transmitting v reached. settable means to adjustablypreset thc'differentialoperating limits atwhich' the instrumentis to be operatively responsive for opening and closing a circuit to which it is connected. and a force transmitting unit within said housing latcd thereto. the improvement comprising within said hou's mg: 7 v

a. a magneticailly actuatable reed switch for opening and closing a circuit to which it is connected;

b. a magnetic member movable by said force transmitting unit toward said reed switch in response to a first form of condition change and away from said reed switch in response to'a second form of condition change to effect opening and closing-of the connected reed switch circuit at the dill'ercntial limits preset by said settable means; and

c. a second switch for c nnection to the circuit to be controlled and operably triggered by actuation of said reed switch. t

2. In the condition responsive controller instrument of claim I in which said second switch is comprised of solid state elements.

J. In the condition responsive controller instrument of claim 2 in which said second switch is mechanically protected in an electrically potting compound.

4. In the condition responsive controller instrument of claim 2 in which the force transmitting unit in Bourdon tube connested via a mechanical linkage to via support for said magresponsive to condition changes for emitting movement corre- 7. in the condition responsive controller instrument of claim sensed condition at which desiredresponse is to be effect'ed: I g t d. a reed switch magnetically actuatablc. between open and closed relation from a normal relationat condition mag- .nitudes below a magnitude selected by said selection means to the other relation at condition magnitudes above a magnitude selected by said selection means;

unit toward and away from said reed switch to effect actuation thereof at a condition magnitude operably selected by said selection means; and

o l.- means to displace the magnetic member'and reed switch locations relative to each other to preset the'instrument between normally open and normally closed operation vfor a condition magnitude operably selected by said selection means.

9. A condition responsive controller instrument according to claim 8 in which said means to displace relative locations of said magnetic member and reed switch includes a stationary support for'said reed switch and means permitting displacement of said reed switch on said support between a first position relative to the magnetic member in which the instrument is operative as normally closed and a second position relative to the magnetic member in which the instrument. is operative v as normally open. 1

and said displacement is angular thereon.

11. A condition responsive controller instrument according to claim 9 in which said force transmitting unit is a Bourdon tube movable in response to condition changes and said magnetic mernlicr is operatively connected to the movable end of said Bourdon tuhe'forrnovemcnt therewith. 

